ABSTRACT
Objective: To study the seroprevalence of SARS-CoV-2 antibodies (AB) in children in the 2nd year of the COVID-19 pandemic in Russia. Materials and methods: Prospective cohort study. The seroprevalence research was conducted among 3670 children aged 1 to 17 y/o from 26 modelling regions of Russia (that have been participating earlier in the five stages of seromonitoring during 2020-2021). The serological testing was carried out in December, 2021. The work was carried out according to a unified methodology set by the Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being with the Pasteur Institute of Epidemiology and Microbiology (Saint Petersburg, Russia). The plasma was obtained from 3 ml of venous blood, in which the level of AB to nucleocapsid (NC), and the SARS-CoV-2 receptor-binding domain (RBD) was determined by immunoferment method using reagents for qualitative and quantitative analysis. Results: The analysis of AB seroprevalence to NC and RBD showed the statistically significant increase in the share of seropositivity to RBD in children of all modelling regions (p<0.05). The most seropositive volunteers contained low levels of AB: 31.3-125.6 BAU/ml NC and 22.6-220 BAU/ml RBD. An increase in the level of AB to NC and RBD was accompanied by a decrease in the percentage of seropositive patients. Evaluating the contribution of children to the level of humoral immunity, convalescents (had been ill shortly before the examination), the «anamnesis» (had been ill at previous stages of seromonitoring) and asymptomatic (had been asymptomatically ill) groups were distinguished. The maximum contribution was made by children with asymptomatic cases of COVID-19 in anamnesis: In 82.3% (95% CI 81.1-83.6), of which 76.9% (95% CI 75.5-78.3) AB detected to RBD. The contribution of children of two other groups to the overall level of humoral immunity was 33 times less. Conclusion: Statistically significant predominance of AB to RBD above AB to NC and their main contribution to the level of humoral immunity to SARS-CоV-2 (p<0.001).
ABSTRACT
The novel coronavirus (SARS-CoV-2) pandemic, dubbed COVID-19, has become one of the most serious challenges for human populations in the vast majority of countries worldwide. Rapid spreading and increased mortality related to it required new approaches to manage epidemic processes on a global scale. One of such approaches was based on analyzing SARS-CoV-2 seroprevalence associated with COVID-19. Our aim was to summarize the results on assessing seroprevalence to the SARS-CoV-2 nucleocapsid antigen (Nc) in residents from 26 regions of the Russian Federation, carried out during the first wave of the COVID-19 epidemic. Materials and methods. Seroprevalence distribution was examined in 26 model regions of the Russian Federation according to the unified method developed by the Rospotrebnadzor with the participation of the Federal State Institution Saint Petersburg Pasteur Research Institute of Epidemiology and Microbiology. Such approach implied formation of a group of volunteer subjects in model geographic region who were tested by ELISA for anti-Nc serum antibody level in peripheral blood. Analyzed primary data obtained in separate regions were either accepted for publication or released. Results. The current paper finalizes the data obtained in all 26 regions of the Russian Federation. The total SARS-CoV-2 seroprevalence was 19.5 (10.0-25.6)% with the maximum and minimum value found in the Kaliningrad Region and the Republic of Crimea, respectively (50.2% vs. 4.3%). A pattern of age-related seroprevalence distribution indicates insignificant predominance of seroprevalence among subjects of 1-17 years old: 22.1 (13.1-31.8)%. Among COVID-19 convalescents positive for SARS-CoV Nc antibodies it reached 60.0 (40.0-73.3)%. The number of contact persons comprised 6285 subjects or 8.5% of total volunteer cohort, with the level of seroprevalence reaching up to 25.3 (17.95-35.8)%. A direct correlation was revealed between levels of seroprevalence in convalescent and contact volunteers. In addition, the reproductive number for SARS-CoV was calculated comprising 5.8 (4.3-8.5) suggesting that one convalescent subject can infect at least 4 healthy individuals. A high level of asymptomatic forms of COVID-19 among seropositive subjects was confirmed empirically comprising up to 93.6 (87.1-94.9)%. Conclusion. A single cross-sectional study performed during 2020 June-August timeframe allowed to assess pattern of sex- and age-related COVID-19 seroprevalence for general population in 26 Russian Federation regions. The data obtained may serve as a basis for the longitudinal cohort investigation with serial subject sampling. The timing and duration of study will be determined by dynamics of ongoing COVID-19 epidemic.